U(VI) hydrazinates: structural and thermal decomposition features

Hydrazine and its derivatives can be used to recover plutonium and uranium from spent nuclear fuel as well as to obtain UO2 or mixed-oxide fuels. Uranium hydrazinates xUO3·yN2H4·zH2O have been synthesized, and their structural peculiarities and phase transitions upon heating have been investigated. It has been found that the elemental composition of U(VI) hydrazinate can be described as UO3·0.3N2H4·1.7H2O. It is a poorly crystalline layered compound with a crystallite size of (14 ± 3) nm, structurally similar to schoepite and ammonium polyuranates with neutral N2H4 molecules between layers of U(VI)-oxygen pentagonal bipyramids. U(VI) is present in the form of a linear UO22+ cation. In an inert atmosphere above 90 °C, xUO3·yN2H4·zH2O decomposes, resulting in partial U(VI) reduction due to the high mobility of hydrazine in the interlayer space or insufficient ratio of N2H4 to U(VI). The weak exothermic effect of the decomposition reaction and absence of combustible gases make the thermal treatment of xUO3·yN2H4·zH2O secure and applicable for nuclear technology.